Note: Descriptions are shown in the official language in which they were submitted.
21~5~,~~
PATENT APPLICATION
Attorney's Docket No. D/91324
LAYERED PHOTORECEPTOR WITH OVERCOATINGS
CONTAINING HYDROGEN BONDED MATERIALS
BACKGROUND OF THE INVENTION
This invention relates in general to electrophotographic imaging
members and, more specifically, to layered photoreceptor structures with
overcoatings containing hydrogen bonded materials and processes for
making and using the photoreceptors.
Electrophotographic imaging members, i.e. photoreceptors,
typically include a photoconductive layer formed on an electrically
conductive substrate. The photoconductive layer is an insulator in the dark
so that electric charges are retained on its surface. Upon exposure to light,
the charge is dissipated.
A latent image is formed on the photoreceptor by first uniformly
depositing an electric charge over the surface of the photoconductive layer
by one of any suitable means well known in the art. The photoconductive
layer functions as a charge storage capacitor with charge on its free surface
and an equal charge of opposite polarity (the counter charge) on the
conductive substrate. A light image is then projected onto the
photoconductive layer. On those portions of the photoconductive layer
that are exposed to light, the electric charge is conducted through the layer
reducing the surface charge. The portions of the surface of the
photoconductor not exposed to light retain their surface charge. The
quantity of electric charge at any particular area of the photoconductive
surface is inversely related to the illumination incident thereon, thus
forming an electrostatic latent image.
The photodischarge of the photoconductive layer requires that
the layer photogenerate conductive charge and transport this charge
through the layer thereby neutralizing the charge on the surface. Two
types of photoreceptor structures have been employed: multilayer
-1-
structures wherein separate layers perform the functions of charge
generation and charge transport, respectively, and single layer
photoconductors which perform both functions. These layers are formed
on an electrically conductive substrate and may include an optional charge
blocking and an adhesive layer between the conductive layer and the
photocondurting layer or layers. Additionally, the substrate may comprise
a non-conducting mechanical support with a conductive surface. Other
layers for providing special functions such as incoherent reflection of laser
light, dot patterns for pictorial imaging or subbing layers to provide
chemical sealing and/or a smooth coating surface may be optionally be
employed.
One common type of photoreceptor is a multilayered device that
comprises a conductive layer, a blocking layer, an adhesive layer, a charge
generating layer, and a charge transport layer. The charge transport layer
can contain an active aromatic diamine molecule, which enables charge
transport, dissolved or molecularly dispersed in a film forming binder. This
type of charge transport layer is described, for example in US-A 4,265,990.
Other charge transport molecules disclosed in the prior art include a variety
of
electron donor, aromatic amines, oxadiazoles) oxazoles, hydrazones and
stilbenes for hole transport and electron acceptor molecules for electron
transport. Another type of charge transport layer has been developed
which utilizes a charge transporting polymer wherein the charge
transporting moiety is incorporated in the polymer as a group pendant
from the backbone of the polymer backbone or as a moiety in the
backbone of the polymer. These types of charge transport polymers
include materials such as poly(N-vinylcarbazole), polysilylenes, and others
including those described, for example, in US-A 4,618,551, 4,806,443,
4,806,444, 4,818,650, 4,935,487, and 4,956,440.
One of the design criteria for the selection of the photosensitive
pigment for a charge generator layer and the charge transporting molecule
for a transport layer is that, when light photons photogenerate holes in the
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pigment, the holes be efficiently injected into the charge transporting
molecule in the transport layer. More specifically, the injection efficiency
from the pigment to the transport layer should be high. A second design
criterion is that the injected holes be transported across the charge
transport layer in a short time; shorter than the time duration between the
exposure and development stations in an imaging device. The transit time
across the transport layer is determined by the charge carrier mobility in the
transport layer. The charge carrier mobility is the velocity per unit field
and
has dimensions of cm2/volt sec. The charge carrier mobility is a function of
the structure of the charge transporting moiety, the concentration of the
charge transporting moiety in the transport layer and the electrically
"inactive" binder polymer in which the charge transport molecule is
dispersed (if the transport layer consists of charge transporting molecules
dispersed in a binder). It is believed that the injection efficiency can be
maximized by choosing a transporting moiety whose ionization potential is
lower than that of the pigment (assuming the charge transporting carriers
are holes). However, low ionization potential molecules may have other
deficiencies, one of which is their instability in an atmosphere of corona
effluents. A copy quality defect resulting from the chemical interaction of
the surface of the transport layer with corona effluents is referred to as
"parking deletion" and is described in detail below.
Photoreceptors are cycled many thousands of times in automatic
copiers, duplicators and printers. This cycling causes degradation of the
imaging properties of photoreceptors, particularly multilayered organic
photoconductors which utilize organic film forming polymers and small
molecule low ionization donor material in the charge transport layers.
Such wear is accelerated when the photoreceptor is utilized in systems
employing abrasive development systems such as single component
development systems. Wear is an even greater problem where a drum is
utilized which has such a small diameter that it must rotate many, many
times merely to form images for each conventional size 8.5 inch by 11 inch
document. Wear of the photoreceptor can be compensated by increasing
the thickness of the charge transport layer. However, large increases in
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2iI83~-5
thickness of the charge transport layer can render the photoreceptor
inoperable at high imaging process speeds because of the very long transit
times of common charge transport layer materials. Also, large decreases in
thickness due to wear can cause dramatic changes in electrical
characteristics in only a few thousand cycles that cannot be readily
compensated by even sophisticated computerized control apparatus.
When the electrophotographic imaging member is utilized in
liquid ink development systems, leaching of small molecules from the
charge transport layer into the liquid development can occur. Loss of the
small molecule material due to leaching causes undesirable deterioration in
electrical properties of the photoreceptor. Also, undesirable crystallization
of the small molecule in the charge transport layer can adversely affect the
electrical imaging characteristics of the photoreceptor.
Reprographic machines utilizing multilayered organic
photoconductors also employ corotrons or scorotrons to charge the
photoconductors prior to imagewise exposure. During the operating
lifetime of these photoconductors they are subjected to corona effluents
which include ozone, various oxides of nitrogen, etc. It is believed that
some of these oxides of nitrogen are converted to nitric acid in the presence
of water molecules present in the ambient operating atmosphere. The top
surface of the photoconductor is exposed to the nitric acid during
operation of the machine and charge transport moieties at the very top
surface of the transport layer are converted to what is believed to be the
nitrated species of the molecules. It is believed that the chemical transition
state species could form an electrically conductive film. However, during
operation of the machine, the cleaning subsystem continuously removes
(by wear) a region of the top surface thereby preventing accumulation of
the conductive species. Unfortunately, such is not the case when the
machine is not operating (i.e. in idle mode) between two large copy runs.
During the idle mode between long copy runs, a specific segment of the
photoreceptor comes to rest (is parked) beneath a corotron that had been
in operation during the long copy run. Although the high voltage to the
corotron is turned off during the time period when the photoreceptor is
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2I1g~4~
parked, some effluents (e.g. nitric acid, etc.) continue to be emitted from
the corotron shield, corotron housing, etc. This effluent emission is
concentrated in the region of the stationary photoreceptor parked directly
underneath the corotron. The effluents render that surface region
electrically conductive. When machine operation is resumed for the next
copy run, image spreading and loss of resolution occurs in the region of the
photoconductor where surface conductivity was increased. Deletion may
also be observed in the loss of fine lines and details in the final print.
Thus,
the corona induced changes primarily occur at the surface region of the
charge transport layer. These changes are manifested in the form of
increased conductivity which results in loss of resolution of the final toner
images. In the case of severe increases in conductivity, there can be regions
of severe deletions in the images. This problem is particularly severe in
devices employing arylamine charge transport molecules such as N,N'-
diphenyi-N,N'-bis(3-methylphenyi)-(1,1'-biphenyl)-4,4'-diamine and charge
transport polymers incorporating diamine transporting moiety.
Although, "parking deletion" is described above, in some cases
deletion might occur in all portions of the photoconductor. This will
depend on the number and type of corotrons employed, the design of the
photoconductor cavity and air-flow patterns around the photoconductor.
Thus, although the charge transport moiety or species meets
most other electrophotographic criteria such as being devoid of traps,
having high injection efficiency from many pigments, ease in synthesizing,
and inexpensive, it encounters serious parking and other deletion problems
when an idle mode is interposed between extended cycling runs.
INFORMATION DISCLOSURE STATEMENT
US-A 4,871,634 to Limburg et al., issued October 3, 1989 - An
electrostatographic imaging member is disclosed which contains at least
one electrophotoconductive layer, the imaging member comprising a
photogenerating material and a hydroxy arylamine compound represented
by a certain formula. The hydroxy aryiamine compound can be used in an
overcoating with the hydroxy arylamine compound bonded to a resin
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2118345
capable of hydrogen bonding such as a polyamide possessing alcohol
solubility.
US-A 4,297,425 to Pai et al., issued October 27, 1981 - A layered
photosensitive member is disclosed comprising a generator layer and a
transport layer containing a combination of diamine and triphenyl
methane molecules dispersed in a polymeric binder.
US-A 4,050,935 to Limburg et al., issued September 27, 1977 - A
layered photosensitive member is disclosed comprising a generator layer of
trigonal selenium and a transport layer of bis(4-diethylamino-2-
methylphenyl)phenylmethane molecularly dispersed in a polymeric binder.
US-A 4,457,994 to Pai et al. et al, issued July 3 1984 - A layered
photosensitive member is disclosed comprising a generator layer and a
transport layer containing a diamine type molecule dispersed in a polymeric
binder and an overcoat containing triphenyl methane molecules dispersed
in a polymeric binder.
US-A 4,281,054 to Horgan et al., issued July 28, 1981 - An
imaging member is disclosed comprising a substrate, an injecting contact,
or hole injecting electrode overlying the substrate, a charge transport layer
comprising an electrically inactive resin containing a dispersed electrically
active material, a layer of charge generator material and a layer of
insulating organic resin overlying the charge generating material. The
charge transport layer can contain triphenylmethane.
US-A 4,515,882 to Mammino et al, issued May 7, 1985 - An
elertrophotographic imaging system is disclosed which utilizes a member
comprising at least one photoconductive layer and an overcoating layer
comprising a film forming continuous phase comprising charge transport
molecules and finely divided charge injection enabling particles dispersed
in the continuous phase, the insulating overcoating layer being
substantially transparent to activating radiation to which the
photoconductive layer is sensitive and substantially electrically insulating
at
low electrical fields.
US-A 4,599,286 to Limburg et al., issued July 8, 1982 - An
electrophotographic imaging member is disclosed comprising a charge
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generation layer and a charge transport layer, the transport layer
comprising an aromatic amine charge transport molecule in a continuous
polymeric binder phase and a chemical stabilizer selected from the group
consisting of certain nitrone, isobenzofuran, hydroxyaromatic compounds
and mixtures thereof. An electrophotographic imaging process using this
member is also described.
In a copending Canadian application entitled "LONG LIFE
PHGTORECEPTOR", filed under No. 2,134,276, an electrophotographic
imaging member is disclosed comprising a substrate, a charge
generating layer, a charge
transport layer, and an overcoat layer comprising a small molecule hole
transporting triphenyl methane having at least one hydroxy functional
group) and a polyamide film forming binder capable of forming hydrogen
bonds with the hydroxy functional groups of the hydroxy triphenyl
methane. This overcoat layer may be fabricated using an alcohol solvent.
This electrophotographic imaging member may be utilized in an
electrophotographic imaging process.
Although acceptable images may be obtained when chemical
triphenyl urethanes are incorporated within the bulk of the charge
transport layers, the photoreceptor can exhibit at least two deficiencies
when subjected to extensive cycling. One is that the presence of the
triphenyl methane in the bulk of the charge transport layer results in
trapping of photoinjected holes from the generator layer into the transport
layer giving rise to higher residual potentials. This can cause a condition
known as cycle-up in which the residual potential continues to increase
with multi-cycle operation. This can give rise to increased densities in the
background areas of the final images. A second undesirable effect due to
the addition of the triphenyl methane in the bulk of the transport layer is
that some of these molecules migrate into the generator layer during the
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A
process of the fabrication of the transport layer. The presence of these
molecules on the surface of the pigment in the generator layer could result
in cyclic instabilities, particularly in long image cycling runs. These two
deficiencies limits the concentration of the triphenyl urethanes that can be
added in the transport layer.
Where photoreceptors are overcoated, intermixing of the
overcoat and the transport layers occur which can render the overcoat very
ineffective. This intermixing leads to the incorporation of hydroxy
triphenyl urethanes in the bulk of the transport layer causing cycle-up.
Also, the intermixing causes a reduction of the concentration of triphenyl
urethanes on the outer surface of the photoreceptor. The concentration of
triphenyl urethanes in the outer surface region of the photoreceptor
prevents the aforementioned deletion.
Thus, there is a continuing need for photoreceptors having
improved resistance to corona effluent induced deletions without
increased densities in the background areas of the final images, migration
of additives into the generator layer during fabrication of the transport
layer, and cyclic instabilities.
SUMMARY OF THE INVENTION
It is, therefore, an object of an aspect of the present
invention to provide an improved electrophotographic imaging member
which overcomes the above-noted deficiencies.
It is another object of an aspect of the present invention
to provide an improved electrophotographic imaging member exhibiting
greater resistance to abrasion during image cycling.
It is yet another object of an aspect of the present
invention to provide an improved electrophotographic imaging member
that resists leaching of components from the charge transport layer
during liquid development.
It is still another object of an aspect of the present
invention to provide an improved electrophotographic imaging member
which reduces crystallization of small molecules in those charge
transport layers which contain a transporting molecule and binder
_g_
It is another object of an aspect of the present invention
to provide an improved electrophotographic imaging member which is
stable against copy defects such as print deletion.
It is yet another object of an aspect of the present
invention to provide an improved electrophotographic imaging member
of greater abrasion resistance.
It is still another object of an aspect of the present
invention to provide an improved electrophotographic imaging member
having greater stability against corona induced chemical changes.
It is another object of an aspect of the present invention
to provide an improved electrophotographic imaging member which
avoids residual charge build up.
It is still another object of an aspect of the present
invention to provide an improved electrophotographic imaging member
which is mechanically stronger.
It is yet another object of an aspect of the present
invention to provide an improved electrophotographic imaging member
having an overcoating free of phase separation of component materials.
Further aspects of the present invention are as follows:
An electrophotographic imaging member comprising a
substrate, a charge generating layer, a charge transport layer, and an
overcoat layer comprising a hole transporting hydroxy arylamine
compound having at least two hydroxy functional groups, a hydroxy
triphenyl methane compound having at least one hydroxy functional group
and a polyamide film forming binder capable of forming hydrogen bonds
with said hydroxy functional groups of said hydroxy arylamine compound
and said hydroxy triphenyi methane compound.
A process for fabricating an electrophotographic imaging
member comprising providing a substrate coated with a charge generating
layer and a charge transport layer comprising charge transporting
molecules dispersed in a solution of an alcohol insoluble polymer binder,
forming on said charge transport layer a coating of a solution comprising a
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hydroxy arylamme compound having at !east two hydroxy functional
groups, a hydroxy triphenyl methane compound having at least one
hydroxy functional group and a polyamide film forming binder capable of
forming hydrogen bonds with said hydroxy functional groups of said
hydroxy arylamine compound and said hydroxy triphenyl methane
compound dissolved in an alcohol solvent, and drying said coating to
remove said alcohol solvent to form a substantially dry overcoat layer.
The foregoing objects and others are accomplished in
accordance with this invention by providing an electrophotographic
imaging member comprising a substrate, a charge generating layer, a
charge transport layer, and an overcoat layer comprising a small molecule
hole transporting aryiamine having at least two hydroxy functional groups,
a hydroxy or multihydroxy triphenyl methane and a polyamide film
forming binder capable of forming hydrogen bonds with the hydroxy
functional groups the hydroxy arylamine and hydroxy or multihydroxy
triphenyl methane. This overcoat layer may be fabricated using an alcohol
solvent. This electrophotographic imaging member may be utilized in an
electrophotographic imaging process.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a structural formula of an aromatic diamine
molecule.
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211~3~5
FIG. 2 illustrates a structural formula of a polycarbonate binder
segment.
FIGS. 3a to 3e illustrate a generic structural formula of a small
molecule hole transporting hydroxy arylamine.
FIG. 4 illustrates structural formula of a direct conjugation
segment.
FIG. 5 illustrates structural formulae of compounds in which
hydroxyl groups are in direct conjugation with nitrogen through a
phenylene ring system.
FIGS. 6 and 7 illustrate structural formulae of hydroxy arylamine
compounds.
FIG. 8 illustrates electron transfer from a stabilizer to an
oxidizing agent.
FIG. 9 illustrates a generic structural formula for hydroxy
triphenyl methane.
FIGS. 10-17 illustrate structural formulae of hydroxy triphenyi
methane compounds.
FIG. 18 illustrates a simplified depiction of hydroxy arylamine
and hydroxy triphenyl amine charge transport molecules hydrogen bonded
to polyamide polymer segments in the overcoat layer of this invention.
FIG. 19 illustrates a structural formula of a polycarbonate binder
segment.
Electrophotographic imaging members are well known in the
art. Electrophotographic imaging members may be prepared by any
suitable technique. Typically, a flexible or rigid substrate is provided with
an electrically conductive surface. A charge generating layer is then
applied to the electrically conductive surface. A charge blocking layer may
optionally be applied to the electrically conductive surface prior to the
application of a charge generating layer. If desired, an adhesive layer may
be utilized between the charge blocking layer and the charge generating
layer. Usually the charge generation layer is applied onto the blocking
layer and a charge transport layer is formed on the charge generation layer.
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This structure may have the charge generation layer on top of or below the
charge transport layer.
The substrate may be opaque or substantially transparent and
may comprise any suitable material having the required mechanical
properties. Accordingly, the substrate may comprise a layer of an
electrically non-conductive or conductive material such as an inorganic or
an organic composition. As electrically non-conducting materials there may
be employed various resins known for this purpose including polyesters,
polycarbonates, polyamides, polyurethanes, and the like which are flexible
as thin webs. An electrically conducting substrate may be any metal, for
example, aluminum, nickel, steel, copper, and the like or a polymeric
material, as described above, filled with an electrically conducting
substance, such as carbon, metallic powder, and the like or an organic
electrically conducting material. The electrically insulating or conductive
substrate may be in the form of an endless flexible belt, a web, a rigid
cylinder, a sheet and the like.
The thickness of the substrate layer depends on numerous
factors, including strength desired and economical considerations. Thus,
for a drum, this layer may be of substantial thickness of, for example, up to
many centimeters or of a minimum thickness of less than a millimeter.
Similarly) a flexible belt may be of substantial thickness, for example, about
250 micrometers, or of minimum thickness less than 50 micrometers,
provided there are no adverse effects on the final electrophotographic
device.
In embodiments where the substrate layer is not conductive, the
surface thereof may be rendered electrically conductive by an electrically
conductive coating. The conductive coating may vary in thickness over
substantially wide ranges depending upon the optical transparency, degree
of flexibility desired, and economic factors. Accordingly, for a flexible
photoresponsive imaging device, the thickness of the conductive coating
may be between about 20 angstroms to about 750 angstroms, and more
preferably from about 100 angstroms to about 200 angstroms for an
optimum combination of electrical conductivity, flexibility and light
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transmission. The flexible conductive coating may be an electrically
conductive metal layer formed, for example, on the substrate by any
suitable coating technique, such as a vacuum depositing technique or
eledrodeposition. Typical metals include aluminum, zirconium, niobium,
tantalum, vanadium and hafnium, titanium, nickel, stainless steel,
chromium, tungsten, molybdenum, and the like.
An optional hole blocking layer may be applied to the substrate.
Any suitable and conventional blocking layer capable of forming an
electronic barrier to holes between the adjacent photoconductive layer and
the underlying conductive surface of a substrate may be utilized.
An optional adhesive layer may applied to the hole blocking
layer. Any suitable adhesive layer well known in the art may be utilized.
Typical adhesive layer materials include, for example, polyesters,
polyurethanes, and the like. Satisfactory results may be achieved with
adhesive layer thickness between about 0.05 micrometer (500 angstroms)
and about 0.3 micrometer (3,000 angstroms). Conventional techniques for
applying an adhesive layer coating mixture to the charge blocking layer
include spraying, dip coating, roil coating, wire wound rod coating, gravure
coating, Bird applicator coating, and the like. Drying of the deposited
coating may be effected by any suitable conventional technique such as
oven drying, infra red radiation drying, air drying and the like.
Charge generator layers may comprise amorphous films of
selenium and alloys of selenium and arsenic, tellurium, germanium and the
like, hydrogenated amorphous silicon and compounds of silicon and
germanium, carbon, oxygen, nitrogen and the like fabricated by vacuum
evaporation or deposition. The charge generator layers may also comprise
inorganic pigments of crystalline selenium and its alloys; Group II-VI
compounds; and organic pigments such as quinacridones, polycyclic
pigments such as dibromo anthanthrone pigments, perylene and perinone
diamines, polynuclear aromatic quinones, azo pigments including bis-, tris-
and tetrakis-azos; and the like dispersed in a film forming polymeric binder
and fabricated by solvent coating techniques.
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Phthalocyanines have been employed as photogenerating
materials for use in laser printers utilizing infrared exposure systems.
Infrared sensitivity is required for photoreceptors exposed to low cost
semiconductor laser diode light exposure devices. The absorption spectrum
and photosensitivity of the phthaiocyanines depend on the central metal
atom of the compound. Many metal phthalocyanines have been reported
and include, oxyvanadium phthalocyanine, chloroaluminum
phthalocyanine, copper phthalocyanine, oxytitanium phthalocyanine,
chlorogallium phthalocyanine, hydroxygallium phthalocyanine magnesium
phthalocyanine and metal-free phthalocyanine. The phthalocyanines exist
in many crystal forms which have a strong influence on photogeneration.
Any suitable polymeric film forming binder material may be
employed as the matrix in the charge generating (photogenerating) binder
layer. Typical polymeric film forming materials include those described, for
example, In U.S. Patent 3,121,006. Thus, typical organic polymeric film
forming binders include thermoplastic and thermosetting resins such as
polycarbonates, polyesters, polyamides, polyurethanes, polystyrenes,
polyarylethers, polyarylsulfones, polybutadienes, polysulfones,
polyethersulfones, polyethylenes, polypropylenes, polyimides,
polymethylpentenes, polyphenylene sulfides, polyvinyl acetate,
polysiioxanes, polyacrylates, polyvinyl acetals, polyamides, polyimides,
amino resins, phenylene oxide resins, terephthalic acid resins, phenoxy
resins, epoxy resins, phenolic resins, polystyrene and acryionitrile
copolymers, polyvinylchloride, vinylchloride and vinyl acetate copolymers,
acrylate copolymers, alkyd resins, cellulosic film formers, poly(amideimide),
styrene-butadiene copolymers, vinylidenechloride-vinylchloride
copolymers, vinylacetate-vinylidenechloride copolymers, styrene-alkyd
resins, polyvinylcarbazole, and the like. These polymers may be block,
random or alternating copolymers.
The photogenerating composition or pigment is present in the
resinous binder composition in various amounts. Generally, however, from
about 5 percent by volume to about 90 percent by volume of the
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21..~~3~5
photogenerating pigment is dispersed in about 10 percent by volume to
about 95 percent by volume of the resinous binder, and preferably from
about 20 percent by volume to about 30 percent by volume of the
photogenerating pigment is dispersed in about 70 percent by volume to
about 80 percent by volume of the resinous binder composition. In one
embodiment about 8 percent by volume of the photogenerating pigment is
dispersed in about 92 percent by volume of the resinous binder
composition. The photogenerator layers can also fabricated by vacuum
sublimation in which case there is no binder.
Any suitable and conventional technique may be utilized to mix
and thereafter apply the photogenerating layer coating mixture. Typical
application techniques include spraying, dip coating, roil coating, wire
wound rod coating, vacuum sublimation and the like. For some
applications, the generator layer may be fabricated in a dot or line pattern.
Removing of the solvent of a solvent coated layer may be effected by any
suitable conventional technique such as oven drying, infrared radiation
drying, airdrying and the like.
The charge transport layer may comprise a charge transporting
small molecule dissolved or molecularly dispersed in a film forming
electrically inert polymer such as a polycarbonate. The term "dissolved" as
employed herein is defined herein as forming a solution in which the small
molecule is dissolved in the polymer to form a homogeneous phase. The
expression "molecularly dispersed" is used herein is defined as a charge
transporting small molecule dispersed in the polymer, the small molecules
being dispersed in the polymer on a molecular scale. Any suitable charge
transporting or electrically active small molecule may be employed in the
charge transport layer of this invention. The expression charge
transporting "small molecule" is defined herein as a monomer that allows
the free charge photogenerated in the transport layer to be transported
across the transport layer. Typical charge transporting small molecules
include, for example, pyrazolines such as 1-phenyl-3-(4'-diethylamino
styryl)-5-(4"- diethylamino phenyl)pyrazoline, diamines such as N,N'-
diphenyl-N,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine,
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21183-~
hydrazones such as N-phenyl-N-methyl-3-(9-ethyl)carbazyl hydrazone and
4-diethyl amino benzaldehyde-1,2-Biphenyl hydrazone, and oxadiazoles
such as 2,5-bis (4-N,N'-diethylaminophenyl)-1,2,4-oxadiazole, stiibenes and
the like. However, to avoid cycle-up in machines with high throughput, the
charge transport layer should be substantially free (less than about two
percent) of triphenyl methane. As indicated above, suitable electrically
active small molecule charge transporting compounds are dissolved or
molecularly dispersed in electrically inactive polymeric film forming
materials. A small molecule charge transporting compound that permits
injection of holes from the pigment into the charge generating layer with
high efficiency and transports them across the charge transport layer with
very short transit times is N,N'-Biphenyl-N,N'-bis(3-methyl phenyl)-(1,1'-
biphenyl)-4,4'-diamine represented by the formula shown in Figure 1.
The electrically inert polymeric binder generally used to disperse
the electrically active molecule in the charge transport layer is a poly(4,4'-
isopropylidene-diphenylene)carbonate (also referred to as bisphenol-A-
polycarbonate) represented by the formula shown in Figure 2. The
electrically inert polymer binder can also be poly(4,4'-cyclohexylidine-
diphenylene) carbonate (referred to as bisphenol-Z polycarbonate)
represented by the formula shown in Figure 16.
Any suitable electrically inactive resin binder insoluble in the
alcohol solvent used to apply the overcoat layer may be employed in the
charge transport layer of this invention. Typical inactive resin binders
include polycarbonate resin, polyester, polyaryiate, polyacrylate, polyether,
polysulfone, and the like. Molecular weights can vary, for example, from
about 20,000 to about 150,000. Any suitable charge transporting polymer
of the type shown in Fig. 12 may also be utilized in the charge transporting
layer of this invention. These electrically active charge transporting
polymeric materials should be capable of supporting the injection of
photogenerated holes from the charge generation material and incapable
of allowing the transport of these holes therethrough.
Any suitable and conventional technique may be utilized to mix
and thereafter apply the charge transport layer coating mixture to the
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~1153~.~
charge generating layer. Typical application techniques include spraying,
dip coating, roll coating, wire wound rod coating, and the like. Drying of
the deposited coating may be effected by any suitable conventional
technique such as oven drying, infra red radiation drying, air drying and the
like.
Generally, the thickness of the charge transport layer is between
about 10 and about 50 micrometers, but thicknesses outside this range can
also be used. The hole transport layer should be an insulator to the extent
that the electrostatic charge placed on the hole transport layer is not
conducted in the absence of illumination at a rate sufficient to prevent
formation and retention of an electrostatic latent image thereon. In
general, the ratio of the thickness of the hole transport layer to the charge
generator layers is preferably maintained from about 2:1 to 200:1 and in
some instances as great as 400:1. The charge transport layer, is
substantially non-absorbing to visible light or radiation in the region of
intended use but is electrically "active" in that it allows the injection of
photogenerated holes from the photoconductive layer, i.e., charge
generation layer, and allows these holes to be transported through itself to
selectively discharge a surface charge on the surface of the active layer.
If desired the electrophotographic imaging member of this
invention may comprise a supporting substrate, a charge transport layer,
charge generating layer and an overcoating layer instead of a supporting
substrate, charge generating layer, a charge transport layer and an
overcoating layer. Where the charge generating layer overlies the charge
transport layer, the components of the charge generating layer should be
insoluble in the alcohol solvent employed to apply the overcoat layer of this
invention.
The overcoat layer of this invention comprises at least a
polyamide film forming binder which is soluble in and coated from alcohol,
a polyhydroxy arylamine charge transporting molecule, and a hydroxy
triphenyl methane molecule which functions both as a stabilizer and as a
charge transporting molecule. All the components utilized in the
overcoating of this invention should be soluble in a common alcohol
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solvent. When at least one component in the overcoating mixture is not
soluble in the solvent utilized, phase separation can occur which would
adversely affect the transparency of the overcoating and electrical
performance of the final photoreceptor.
Any suitable alcohol soluble polyamide film forming binder
capable for forming hydrogen bonds with hydroxy functional materials
may be utilized in the overcoating of this invention. The expression
"hydrogen bonding" is defined as an attractive force or bridge occurring
between the polar hydroxy containing arylamine and a hydrogen bonding
resin in which a hydrogen atom of the polar hydroxy arylamine is attracted
to two unshaved electrons of a resin containing polarizable groups. The
hydrogen atom is the positive end of one polar molecule and forms a
linkage with the electronegative end of the other polar molecule. The
polyamide utilized in the overcoating of this invention should also have
sufficient molecular weight to form a film upon removal of the solvent and
also be soluble in alcohol. Generally, the weight average molecular
weights of polyamides vary from about 5,000 to about 1,000,000. Since
some polyamides absorb water from the ambient atmosphere, its electrical
property may vary to some extent with changes in humidity in the absence
of a polyhydroxy arylamine charge transporting monomer, the addition of
polyhydroxy arylamine charge transporting monomer minimizes these
variations. The alcohol soluble poiyamide should be capable of dissolving
in an alcohol solvent which also dissolves the hole transporting small
molecule having multiple hydroxy functional groups. The polyamide
polymers of this invention are characterized by the the presence of the
amide group -CONH. Typical polyamides include the various Elvamide
resins which are nylon multipolymer resins, such as the alcohol soluble
Elvamide and Elvamide TH resins. Elvamide resins are available from E.l.
DuPont Nemours and Company. Other examples of polyamides include
Elvamide 8061, Elvamide 8064, Elvamide 8023.
When the overcoat layer contains only polyamide binder
material, the layer tends to absorb moisture from the ambient atmosphere
-18-
._. 21.~5~~~
and becomes soft and hazy. This adversely affects the electrical properties,
the rycling life, and sensitivity of the overcoated photoreceptor.
Any suitable polyhydroxy diaryl amine small molecule charge
transport material having at least two hydroxy functional groups may be
utilized in the overcoating layer of this invention. A preferred small
molecule hole transporting material can be represented by the following
formula shown in Figure 3a.
wherein
m is 0 or 1,
Z is selected from the group consisting of the groups shown in
Figure 3b,
n is 0 or 1,
Ar is selected from the group consisting of the groups shown in
Figure 3c,
R is selected from the group consisting of -CH3, -C2H5, -C3H~, and
-C4H9,
Ar' is selected from the group consisting of the groups shown in
Figure 3e,
X is selected from the group consisting of the groups shown in
Figure 3f,
s is 0, 1 or 2,
the dihydroxy arylamine compound being free of any direct conjugation
between the -OH groups and the nearest nitrogen atom through one or
more aromatic rings.
-19-
2~I834~
The expression "direct conjugation" is defined as the presence
of a segment, having the formula shown in Figure 4, in one or more
aromatic rings directly between an -OH group and the nearest nitrogen
atom. Examples of direct conjugation between the -OH groups and the
nearest nitrogen atom through one or more aromatic rings include a
compound containing a phenylene group having an -OH group in the ortho
or para position (or 2 or 4 position) on the phenylene group relative to a
nitrogen atom attached to the phenylene group or a compound containing
a polyphenylene group having an -OH group in the ortho or para position
on the terminal phenylene group relative to a nitrogen atom attached to
an associated phenylene group.
The two structures shown in Figure 5 are illustrative examples of
specific compounds in which the hydroxyl group is in direct conjugation
with the nitrogen through a phenylene ring system.
Typical polyhydroxy arylamine compounds utilized in the
overcoat of this invention include, for example:
N,N'-Biphenyl-N,N'-bis(3-hydroxyphenyl)-[1,1'-biphenyl]-4,4'-diamine;
N,N,N',N',-tetra(3-hydroxyphenyl)-[1,1'-biphenyl]-4,4'-diamine;
N,N-d i(3-hyd roxyphenyl)-m-tol a id ine;
1,1-bis-[4-(di-N,N-m-hydroxyphenyl)-aminophenyl]-cyclohexane;
1,1-bis[4-(N-m-hydroxyphenyl)-4-(N-phenyl)-aminophenyl]-cyclohexane;
Bis-(N-(3-hydroxyphenyl)-N-phenyl-4-aminophenyl)-methane;
Bis((N-(3-hydroxyphenyl)-N-phenyl)-4-aminophenyl]-isopropyiidene;
N,N'-Biphenyl-N,N'-bis(3-hydroxyphenyl)-[1,1':4',1 "-terphenyl]-4,4"-
diamine;
9-ethyl-3.6-bis[N-phenyl-N-3(3-hydroxyphenyl)-amino]-carbazole;
2,7-bis[N,N-di(3-hydroxyphenyl)-amino]-fluorene;
1,6-bis[N,N-di(3-hydroxyphenyl)-amino]-pyrene;
1,4-bis(N-phenyl-N-(3-hydroxyphenyl)]-phenylenediamine.
Structural formulae for some of these polyhydroxy arylamine compounds
are illustrated in Figures 6 and 7.
Typical hydroxy arylamine compounds containing direct
-20-
conjugation between the -OH groups and the nearest nitrogen atom
through one or more aromatic rings include, for example:
N,N'-Biphenyl-N-N'-bis(4-hydroxy phenyl)(1,1'-biphenyl]-4,4'-diamine
N,N,N',N',-tetra(4-hydroxyphenyl)-(1,1'-biphenyl]-4,4'-diamine;
N,N-di(4-hydroxyphenyl)-m-toluidine;
1,1-bis-[4-(di-N,N-p-hydroxyphenyl)-aminophenyl]-cyclohexane;
1,1-bis[4-(N-o-hydroxyphenyl)-4-(N-phenyl)-aminophenyl]-cydohexane;
Bis-(N-(4-hydroxyphenyl)-N-phenyl-4-aminophenyl)-methane;
Bis((N-(4-hydroxyphenyl)-N-phenyl)-4-aminophenyi]-isopropylidene;
Bis-N,N-[(4'-hydroxy-4-( 1,1'-biphenyl)]-aniline;
Bis-N,N-((2'-hydroxy-4-(1,1'-biphenyl)]-aniline and the like.
Charge transporting polyhydroxy arylamine compound are known and are
described, for example in US-A 4,871,634.
The overcoating layer of this invention also contains at least one
hydroxy triphenyl methane stabilizer material. The hydroxy triphenyl
methane stabilizer material should contain at least one hydroxy functional
group and, more preferably, at least two hydroxy functional groups. There
does not appear to be any limitation as to the maximum number of hydroxy
functional groups attached to the hydroxy triphenyl methane stabilizer
molecule. The hydroxyl groups attached to the triphenyl methane family of
molecules interact so strongly with polyamide binders capable of forming
hydrogen bonds that they cannot separate. Additionally, these hydroxy
triphenyl methane molecules are soluble in alcohol which must also be used
as the solvent for the polyamide binder and hydroxy arylamines. The
presence of hydroxy triphenyl urethanes in the overcoat increases its
stability against deletion compared to overcoats containing only the
hydroxy arylamine and polyamide binder. The overcoat composition of
polyhydroxy arylamine small molecule transport molecule, hydroxy
triphenyl methane and polyamide provides sufficient charge transport
capabilities to the overcoat to prevent residual build up and improved
stability against corona induced chemical changes. Although the precise
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2118345
nature for stabilization to the oxidizing environment of corona is not
known, it is believed that the stabilization mechanism may initially involve
an electron transfer from the stabilizer to the oxidizing agent, herein
referred to as Ox, followed by a disproportion reaction of the triphenyl
methane moiety. An example this is illustrated in Figure 8.
Hydroxy triphenyl methane stabilizer molecules of this invention
is represented by the generic formula shown in Figure 9 wherein R~, R2, R3,
and R~, are independently selected from the group consisting of:
-CH3, -H, -OH, -N(CH2CH3),
Rg
wherein Rg, Rg and Rip are independently
- C - Rg selected from H, -(CH2-)n"' CH3 wherein n"'
is an integer from 0 to 6,
Rio
R5
wherein R5 and R6 are independently
N selected from the group consisting of
H, -(CH2)~~-~-CH3 wherein n"" is an
integer from 0 to 6,
R6
-22-
~1183~~
R~
wherein R~ is independently selected from
H, -(CH2)n--~--CH3 wherein n""' and m are
-N an integer from 0 to 6,
~CE"~2)m~H3
-N(CH3)CH2CH20H, -N(CH2)nCH3(CH2)~~OH wherein n is an
integer from 0 to 6 and n' is an integer from 1 to 6,
-N[(CHZ)n"CH20H]2 wherein n" is an integer from 0 to 6,
wherein at (east one or more of R~, R2, R3, or R4 must contain at (east one
hydroxy group, and wherein at least one or more of R~, R2, R3, or R4 must
contain at least one amino group.
Typical hydroxy triphenyl methane stabilizer stabilizer molecules
are represented by the formulae in Figures 10 through 17.
In the Figure 18, a representation is illustrated of hydrogen bond
formation between hydroxy groups of polyhydroxy arylamine hole
transport molecules, hydroxy triphenyi amine charge transport molecules,
and amide linkages of polyamide binder molecules capable of forming
hydrogen bonds with the hydroxy functional groups of the hole transport
molecules.
Any suitable alcohol may be employed to apply the overcoating
composition of this invention. The alcohol selected should dissolve the
polyhydroxy arylamine, the hydroxy triphenylmethane, and the polyamide
utilized in the overcoating layer. The alcohol solvent should not dissolve
any binder in the underlying layer. The use of an alcohol solvent minimizes
the impact of the coating process on the environment. The alcohol should
contain at least one hydroxy functional group per molecule. Typical
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~1~~345
alcohols containing at least one hydroxy functional group per molecule
include, for example, isopropanol, methanol, ethanol, butanol, n-propanol,
and the like. Alcohols with more than one hydroxy group per molecule
include, for example) glycol, and the like. Satisfactory results may be
achieved when the amount of alcohol utilized is between about 99 percent
by weight and about 70 percent by weight based on the total weight of the
coating composition. Generally, the optimum amount of alcohol utilized
depends upon the particular type of coating process utilized to apply the
overcoating material.
A simplified depiction of polyhydroxy arylamine and hydroxy
triphenyl amine charge transport molecules hydrogen bonded to
polyamide polymer segments in the overcoat layer of this invention is
illustrated in Figure 16 where "AA" represents polyhydroxy arylamine
molecules and "TP" represents polyhydroxy triphenylmethane molecules.
The concentration of the polyhydroxy arylamine charge
transporting molecules in the overcoat can be between 20 and about 50
percent by weight based on the total weight of the dried overcoat. When
the proportion of polyhydroxy arylamine small molecule hole transporting
molecule in the overcoating is less than about 20 percent by weight, a
residual voltage may develop with cycling resulting in background
problems. When the proportion of poly hydroxy arylamine small molecule
charge transport material in the overcoating layer exceeds about 50
percent by weight based on the total weight of the overcoating layer,
crystallization may occur resulting in residual cycle-up. In addition,
mechanical properties, abrasive wear properties are negatively impacted.
The presence of excess polyhydroxyarylamine material can increase the
layers susceptibility to corona induced deletions. The concentration of the
hydroxy triphenyl methane molecule in the overcoat layer is between
about 0.5 percent and about 50 percent by weight based on the total
weight of the dried overcoat. When less than about 0.5 percent by weight
of hydroxy triphenyl methane molecule is present in the overcoat, the
beneficial results of resistance to print deletion is less pronounced. When
the proportion of hydroxy triphenylmethane small molecule charge
-24-
._ ~11~~~~
transport material in the overcoating layer is greater than about 20 percent
by weight based on the total weight of the overcoating layer, increases in
residual voltages can be seen with long term cycling. In addition,
mechanical and abrasive wear properties can be negatively impacted. The
total combined concentration of the hydroxy aryl amine and hydroxy triaryl
methane should be between about 5 percent and about 50 percent by
weight based on the total weight of the dried overcoat, the remainder
normally being the polyamide binder.
Any suitable coating technique may be utilized to form the
overcoating layer. Typical coating techniques include spraying, extrusion
coating, roll coating, veneer coating, dip coating, slide coating, slot
coating, wire wound rod coating, and the like.
Any suitable technique may be utilized to dry the overcoating.
Typical drying techniques include oven drying, forced air oven drying,
radiant heat drying, and the like.
The thickness of the dried overcoat layer should be uniform and
continuous. It can range in thickness from a mono molecular thickness up
to a maximum thickness about about 10 micrometers. Generally, thicker
coatings may be utilized for slower electrophotographic copier and
printers.
If desired, the outer surface of the overcoating layer may be
imparted with a texture to minimize the formation of moray patterns. The
texture may be achieved by any suitable means such as embossing,
regulation of drying conditions, and the like.
Generally, when large amounts of a charge transporting
molecule material is added to an overcoating layer, the strength of the
overcoating layer is reduced. Surprisingly, the overcoating layer of this
invention becomes tougher when large amounts of small molecule
arylamine and triphenyl methane charge transport material having at least
two hydroxy functional groups are incorporated into the overcoating layer
of this invention. When arylamine charge transport material having at
least two hydroxy functional groups and triphenyl methane charge
transport material having at least one hydroxy functional group are
-2 S-
~1I834~
blended with polyamide binder capable of hydrogen bonding to achieve
hydrogen bonding, the combination of materials restricts the absorption of
atmospheric moisture into the polyamide polymer thereby eliminating the
plasticizing effect of the water. Moisture tends to lessen overcoating
abrasion and wear resistance when the vvercoating contains only the
polyamide. Unlike coatings containing small molecule charge transport
material dissolved or molecularly dispersed in polycarbonate binder, the
hydrogen bonded overcoat layer is compositionally stable and does not
phase separate even when exposed to liquid ink media.
The film forming binder for the transport layer should not
dissolve in the alcohol solvent selected for the overcoating layer. For
example, charge transport layer binders such as polycarbonates do not
dissolve in alcohol. Thus, for example, poly(4,4'-isopropylidene-
diphenylene) carbonate (i.e. bisphenol-A-polycarbonate) or poly(4,4'-
cyclohexylidine-diphenylene) carbonate (also referred to as bisphenol-Z-
polycarbonate), having a structure represented by the formula shown in
Figure 19, do not dissolve in alcohols such as ethanol, n-propanol)
isopropanol, methanol, butanol, and the like. Bisphenol-A-polycarbonate
dissolves in methylene chloride and bisphenol-Z-polycarbonate is soluble in
toluene. Other polymers insoluble in alcohols include, for example
polystyrene, polyethercarbonate, polyesters, and the like. The expression
"soluble" as employed herein is defined as capable of forming a solution
with which a film can be applied to a surface and dried to form a
continuous coating. The expression "insoluble" as employed herein is
defined as not capable of forming a solution so that the solvent and the
solid remain in two separate phases and a continuous coating cannot be
formed. Molecular weights of the polymers can vary, for example, from
about 20,000 to about 150,000.
The composition and materials employed in the overcoat layer
must meet several requirements: (1) it should be charge transporting to
prevent a residual build up across the overcoat, and (2) it should not
intermix into the charge transport layer during the process of fabricating
the overcoat. The second requirement can be met by the judicious selection
-26-
211~3~5
of binders for the charge transport layer and the overcoat layers whereby
the polymer binder for the overcoat is soluble in a solvent in which the
polymer binder for the charge transport layer is insoluble.
Other suitable layers may also be used such as a conventional
electrically conductive ground strip along one edge of the belt or drum in
contact with the conductive surface of the substrate to facilitate connection
of the electrically conductive layer of the photoreceptor to ground or to an
electrical bias. Ground strips are well known and usually comprise
conductive particles dispersed in a film forming binder.
In some cases an anti-curl back coating may be applied to the
side opposite the photoreceptor to provide flatness and/or abrasion
resistance for belt or web type photoreceptors. These anti-curl back
coating layers are well known in the art and may comprise thermoplastic
organic polymers or inorganic polymers that are electrically insulating or
slightly semiconducting.
The photoreceptor of this invention may be used in any
conventional electrophotographic imaging system. As described above,
electrophotographic imaging usually involves depositing a uniform
electrostatic charge on the photoreceptor, exposing the photoreceptor to a
light image pattern to form an electrostatic latent image on the
photoreceptor, developing the electrostatic latent image with
electrostatically attractable marking particles to form a visible toner image,
transferring the toner image to a receiving member and repeating the
depositing, exposing, developing and transferring steps at least once.
A number of examples are set forth hereinbelow and are
illustrative of different compositions and conditions that can be utilized in
practicing the invention. All proportions are by weight unless otherwise
indicated. It will be apparent, however, that the invention can be practiced
with many types of compositions and can have many different uses in
accordance with the disclosure above and as pointed out hereinafter.
-27-
~1183~5
TEST PROCEDURES UTILIZED IN FOLLOWING EXAMPLES
Wear Characterization
A turntable device was fitted with a polyurethane blade
configured in the doctor mode, the blade was adjustable for reproducible
setting of the nip gap, a metered dispenser was used to feed specific
quantities of a single component developer from the 5012, 5014 and 1012
electrophotographic imaging machines were used in the abrading agent, at
predetermined intervals onto a rotating sample platen, and a tachometer
and timer were used to calculate the number of elapsed sample rotations.
This device was employed to test wear of materials by abrasion. Wear was
calculated in terms of nanometers/kilocycles of rotation (nm/Kc).
Reproducibility of calibration standards was about t 2nm/Kc. Sample wear
was measured by an interference measuring device, known as an Otsuka
gauge.
Scanner Characterization
Each photoconductor device to be evaluated is mounted on a
cylindrical aluminum drum substrate which is rotated on a shaft. The device
is charged by a corotron mounted along the periphery of the drum. The
surface potential is measured as a function of time by capacitively coupled
voltage probes placed at different locations around the shaft. The probes
are calibrated by applying known potentials to the drum substrate. The
devices on the drums are exposed by a light source located at a position
near the drum downstream from the corotron. As the drum is rotated, the
initial (pre-exposure) charging potential is measured by voltage probe 1.
Further rotation leads to the exposure station, where the photoconductor
device is exposed to monochromatic radiation of known intensity. The
device is erased by light source located at a position upstream of charging.
The measurements made include charging of the photoconductor device in
a constant current or voltage mode. The device is charged to a negative
polarity corona. As the drum is rotated, the initial charging potential is
measured by voltage probe 1. Further rotation leads to the exposure
_28_
._ 21~.~3~~
station, where the photoconductor device is exposed to monochromatic
radiation of known intensity. The surface potential after exposure is
measured by voltage probes 2 and 3. The device is finally exposed to an
erase lamp of appropriate intensity and any residual potential is measured
by voltage probe 4. The process is repeated with the magnitude of the
exposure automatically changed during the next cycle. The photodischarge
characteristics is obtained by plotting the potentials at voltage probes 2
and 3 as a function of light exposure. The charge acceptance and dark
decay can also be measured in the scanner.
Parking Deletion Test
A negative corotron is operated (with high voltage connected to
the corotron wire) opposite a grounded electrode for several hours. The
high voltage is turned off, and the corotron is placed (or parked) for thirty
minutes on a segment of the photoconductor device being tested. Only a
short middle segment of the device is thus exposed to the corotron
effluents. Unexposed regions on either side of the exposed regions are
used as controls. The photoconductor device is then tested in a scanner for
positive charging properties for systems employing donor type molecules.
These systems are operated with negative polarity corotron in the latent
image formation step. An electrically conductive surface region (excess
hole concentration) appears as a loss of positive charge acceptance or
increased dark decay in the exposed regions (compared to the unexposed
control areas on either side of the short middle segment) Since the
electrically conductive region is located on the surface of the device, a
negative charge acceptance scan is not affected by the corotron effluent
exposure (negative charges do not move through a charge transport layer
made up of donor molecules). However, the excess carriers on the surface
cause surface conductivity resulting in loss of image resolution and, in
severe cases, causes deletion.
_29_
21183~~
EXAMPLE I
A 20 cm (8 inch) x 20 cm (8 inch) aluminum plate wear plate was
primed with 0.1 percent by weight Elvacite 2008 in 90:10 weight ratio of
isopropyl alcohol and water using a #3 Mayer rod and thereafter air dried
in a hood. 10.0 grams of a 10 percent by weight solution of polyamide
(Elvamide 8061, available form E.I. du Pont de Nemours & Co.) in 80:20
weight ratio solvent of methanol and propanol and 1.0 gram of N,N'-
diphenyl-N,N'-bis(3-hydroxyphenyl)-[1,1'-biphenyl]-4,4'-diamine (a
dihydroxy aryiamine) were roll milled about 2 hours and then allowed to
stand several hours before use. This coating solution was applied to the
primed plate using a #75 Mayer rod. The applied film was dried under
cover in a hood (fan off), for about 30 minutes to I hour. The cover was
removed and the sample was oven dried at 70°C for I hour and then at
125°C for 2 hours. The dried coating thickness was 25.0 micrometers.
When
subjected to the wear characterization test, the wear data was found to be
8 manometers of wear/k cycle.
EXAMPLE II
The procedures described in Example I was repeated with the
same materials and conditions except that 8.0 grams of a 0.1 percent by
weight solution of polyamide (Elvamide 8061, available form E.I. du Pont de
Nemours & Co.) in 90:10 weight ratio of methanol and propanol and 0.8
gram of N,N'-diphenyi-N,N'-bis(3-hydroxyphenyl)-[1,1'-biphenyl]-4,4'-
diamine (a dihydroxy arylamine) were roll milled about 2 hours and then
allowed to stand several hours before use. This coating solution was
applied to the primed plate using a #60 Mayer rod. The applied film was
dried under cover in a hood (fan off) for about about I hour. The cover was
removed and the sample was oven dried at 125°C for 45 minutes. The
dried
coating thickness was 9.5 micrometers. When subjected to the wear
characterization test, the wear data was found to be 6 manometers of
wear/k cycle.
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2118345
EXAMPLE III
The procedures described in Example I was repeated with the
same materials and conditions except that 7.0 grams of a 10 percent by
weight solution of polyamide (Elvamide 8064, available form E.I. du Pont de
Nemours & Co.) in 90:10 weight ratio of methanol and 1,1,2
trichloroethane and 0.7 gram of N,N'-Biphenyl-N,N'-bis(3-hydroxyphenyl)-
[1,1'-biphenyl]-4,4'-diamine (a dihydroxy arylamine) were roll milled about
1 hour and then allowed to stand two hours before use. This coating
solution was applied to the primed plate using a #75 Mayer rod. The
applied film was air dried under cover in an open hood (fan off) for about
30 minutes and then in the hood with the fan on for about 30 minutes. This
was followed by one hour of drying in a 50°C oven followed by 2 hours
in
an oven at 125°C. The dried coating thickness was 20.5 micrometers.
When
subjected to the wear characterization test, the wear data was found to be
7 nanometers of wear/k cycle.
EXAMPLE 1V
A primed sample plate as described in Example I was prepared.
grams of a 10 percent by weight solution of polycarbonate (Makrolon)
and 1 gram of N,N'-bis(3-methyl-phenyl)-[1,1'biphenyl]-4,4'-diamine were
mixed for about 24 hours. The coating solution was applied to the primed
plate using a #50 Mayer rod. The applied film was dried in a forced air
oven at 80°C for 30 minutes. The dried coating thickness was 15
micrometers. When subjected to the wear characterization test, the wear
data was found to be 27 nanometers of wear/k cycle.
EXAMPLE V
A photoreceptor sample was prepared by forming coatings
using conventional techniques. The sample had a charge generator layer
containing photoconductive particles dispersed in a binder and a charge
transport layer containing 40 percent by weight N,N'-Biphenyl-N,N'-bis(3-
methyl-phenyl)-(1,1'biphenyl)-4,4'-diamine in 60 percent by weight
polycarbonate polycarbonate resin [poly(4,4'-isopropylidene-diphenylene
-31-
21.1~~4~
carbonate, available as Makrolon R from Farbenfabricken Bayer A. G.]. The
N,N'-Biphenyl-N,N'-bis(3-methyl-phenyl)-(1,1'biphenyl)-4,4'-diamine is an
electrically active aromatic diamine charge transport small molecule
whereas the polycarbonate resin is an electrically inactive film forming
binder. Half of the length of the sample was coated with an overcoat of 50
percent by weight polyamide (Elvamide 8061, available from duPont de
Nemours & Co.), 45 percent by weight N,N'-Biphenyl-N,N'-bis(3-
hydroxyphenyl)-(1,1'-biphenyl]-4,4'-diamine (a dihydroxy arylamine), 5
percent by weight triphenyl methane (formula illustrated in Figure 14)
dissolved in 1:1 methanol/n-propanol to form a 20 percent by weight solids
solution. The coated sample was dried in a forced air oven to form an
overcoat layer. Electrical tests for PIDC characteristics were conducted in
regions with and without overcoat. The residual on the overcoat side was
equivalent to that measured in the non-overcoated side even after many
cycles. The print quality was equivalent.
EXAMPLE VI
To determine whether the half coated with the overcoat of this
invention would create problems in high RH atmosphere, print testing was
carried out after conditioning the drum in 27°C (80°F), 80
percent RH
atmosphere. The print quality was equivalent to that obtained on the
uncoated half.
EXAMPLE VII
Wear testing was carried out on a sample coated with charge
transport transport layer containing 40 percent by weight N,N'-diphenyl-
N,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine and 60 percent by
weight polycarbonate. Half of the charge transport layer on the sample
had no overcoat and the other half was coated with an overcoat of 50
percent by weight polyamide (Elvamide 8061, available from Du Pont de
Nemours & Co.), 45 percent by weight N,N'-Biphenyl-N,N'-bis(3-
hydroxyphenyl)-[1,1'-biphenyl]-4,4'-diamine (a dihydroxy arylamine), 5
percent by weight triphenyl methane (formula illustrated in Figure 14)
-32-
dissolved in 1:1 methanol/n-propanol. After coating and drying, the wear
rate was determined using the test above. It was found that wear in the
overcoated region was reduced by a factor of 3-4 as compared to the region
not overcoated.
EXAMPLE VIII
Corona induced deletion characteristic tests were conducted for
a drum identical to that described in Example VII. This test is described
above in the introduction to the working examples. Dramatic
improvements were observed with the overcoated side.
EXAMPLE IX
Liquid ink compatibility of a drum identical to that described in
Example VII was tested by soaking the drum in Isopar. Molecules of N,N'-
diphenyl-N,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine started
leaching out within minutes in the region without the overcoat whereas
the side with the overcoat remained stable even after days of soaking.
EXAMPLE X
An organic photoreceptor drum containing a charge generating
layer of photoconductive particles dispersed in a binder and a charge
transport layer containing N,N'-Biphenyl-N,N'-bis(3-methylphenyl)-(1,1'-
biphenyl)-4,4'-diamine in polycarbonate was overcoated over one half of its
surface with an overcoating containing 50 percent by weight N,N'-
diphenyl-N,N'-bis(3-hydroxyphenyl)-(1,1'-biphenyl]-4,4'-diamine and 50
percent by weight polyamide (Elvamide 8061) having a final dry film
thickness of 3.0 micrometers. Extensive print testing to several thousand
continuous copies showed evidence of fine line deletion only on the
overcoated portion of the drum surface.
EXAMPLE XI
An organic photoreceptor drum containing a charge generating
layer of photoconductive particles dispersed in a binder and a charge
-33-
transport layer containing N,N'-Biphenyl-N,N'-bis(3-methyl phenyl)-(1,1'-
biphenyl)-4,4'-diamine in polycarbonate was overcoated over one half of its
surface with an overcoating containing 40 percent by weight N,N'-
diphenyl-N,N'-bis(3-hydroxyphenyl)-[1,1'-biphenyl]-4,4'-diamine, 10
percent by weight dihydroxy triphenyl methane and 50 percent by weight
polyamide (Elvamide 8061) having a final dry film thickness of 3.0
micrometers. Extensive print testing to several thousand continuous copies
showed no deletion on the overcoated portion of the drum identical to the
non-overcoated control area.
Although the invention has been described with reference to
specific preferred embodiments, it is not intended to be limited thereto,
rather those skilled in the art will recognize that variations and
modifications may be made therein which are within the spirit of the
invention and within the scope of the claims.
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